When the City Hall Tower was built in downtown Philadelphia, it was topped by a "colossal" bronze figure of William Penn.
The structure - more than 500 feet in height and encircled with a ring of arc lights which burn the night long" - was dedicated on July 4, 1897, which was also when the lights were first turned on.
Within a few weeks it was known to be a hazard for migratory birds. The first report of a dead bird was given in the Philadelphia Evening Bulletin, and had been found at the balcony just below the lights of the tower.
William L. Baily investigated and found that it was a young Sora rail. He also noted: "This was the first bird that had flown against the tower since the lamps had been lighted."
The potential to note other instances piqued his interest, so he continued to monitor the site for bird-strikes for the next three years. His initial report of findings was read before the "Seventeenth Congress" of the American Ornithologists' Union meeting on November 15, 1899 at Philadelphia. A subsequent article was issued in 1900 by the Delaware Valley Ornithological Club of Philadelphia.
Mr. Baily's article titled "Migration Data on City Hall Tower" noted that: "Unintentionally this beautiful circle, crowning the highest point for miles around, has been the destroyer of many birds during their nocturnal migrations between their winter and summer homes. As much as we deplore this unfortunate destruction, we have been able at the same time to obtain some interesting data upon the subject of migration."
He noted species of the dead birds found (with others expected to have been taken away by passer-bys, eaten by cats or dogs, or otherwise removed and therefore not considered), the season of occurrence, kept weather-related notes, and observed bird behavior around the monument.
"In 1987, during the fall observations, nearly the whole month of September was clear and few birds were led astray into the light, and only thirty struck between August 23rd and November 8th. In the spring of 1898 Penn's collection only amounted to six birds. In the fall, the first two weeks of September were so warm that there was practically no migration until the 15th, when it was sudden and soon over, netting thirty-one victims.
"The present year (1899) the great clock, with an illuminated face over twenty-five feet in diameter, made its appearance, but luckily for the birds, the lights around the tower were turned off from May 2 to 16, and all the birds escaped but ten.
"The fall, however, the great parade and the Industrial Exhibition were special occasions for illumination, when four festoons of lamps were swung from the rim of Penn's hat to the balcony, and the gleanings from August 23 to October 31 amounted to four hundred and fifty-two birds. If, like the light-houses, there was a cylinder of glass around the outside of the light this slaughter would have been enormous. As it is, many of the birds approach the tower without striking, and I have watched them fly between the lights, circle the tower and then disappear into the darkness without in the least endangering their lives."
In his report, Mr. Baily made some comparisons of when old versus young birds were found, and briefly considered weather conditions and how they would be a variable.
The following species were collected during the spring and autumn seasons from August 27, 1897 to October 31, 1899. Species are listed alphabetically instead of in the order presented by the article.
Philadelphia City Hall ca. 1899. Image available at Wikipedia.
- American Kestrel (sparrow hawk): 1
- American Redstart: 16
- Bay-breasted Warbler: 1
- Black-and-white Warbler: 12
- Black-billed Cuckoo: 2
- Black-throated Blue Warbler: 12
- Black-throated Green Warbler: 24
- Blackburnian Warbler: 10
- Blackpoll Warbler: 23
- Bobolink: 1
- Brown Creeper: 1
- Brown Thrasher: 3
- Cape May Warbler: 1
- Cedar Waxwing: 4
- Chestnut-sided Warbler: 2
- Chipping Sparrow: 14
- Common Yellowthroat (Maryland yellow-throat): 158
- Connecticut Warbler: 12
- Dark-eyed Junco (slate-colored junco): 6
- Eastern Phoebe: 1
- Eastern Towhee: 2
- Eastern Wood-Pewee: 1
- Field Sparrow: 6
- Golden-crowned Kinglet: 1
- Grasshopper Sparrow: 2
- Gray Catbird: 3
- Horned Grebe: 1
- House Wren: 1
- Indigo Bunting: 6
- Magnolia Warbler: 5
- Marsh Wren: 3
- Mourning Dove: 2
- Myrtle Warbler: 34
- Nashville Warbler: 1
- Northern Flicker (flicker): 6
- Northern Parula (parula warbler): 67
- Ovenbird: 7
- Palm Warbler: 1
- Pine Warbler: 5
- Prairie Warbler: 1
- Red-breasted Nuthatch: 6
- Red-eyed Vireo: 16
- Ruby-crowned Kinglet: 2
- Ruddy Duck: 1
- Savannah Sparrow: 2
- Scarlet Tanager: 2
- Solitary Vireo (blue-headed vireo): 1
- Song Sparrow: 1
- Sora: 1
- White-eyed Vireo: 1
- White-throated Sparrow: 1
- Wood Thrush: 1
- Yellow-bellied Cuckoo: 4
- Yellow-bellied Sapsucker: 1
- Yellow-breasted Chat: 3
- Yellow? Warbler (yellow palm warbler): 26
Overall, 529 specimens representing 56 species were gathered, including 21 species of warblers and six kinds of sparrows, with most of the others typical songbirds of the eastern Pennsylvania region.
This report is an important account which adds significantly to the early history of bird-strikes in American cities.
The City Hall Tower is still present in Philadelphia, though whether it is still a hazard for migratory birds is not known.